1. Field of the Invention
The present invention relates to a signal processing apparatus, and more particularly to a signal processing apparatus which permits a signal processing program for imparting an effect to a signal from an electronic musical instrument to be rewritten.
2. Description of the Related Art
A conventional signal processing apparatus for use in an electronic musical instrument has a memory having a program stored inside, and processes a received signal within one cycle of a sampling clock according to the program. In the case of receiving a musical tone signal with eight polyphonic sounds from an electronic musical instrument, for example, a time-dividing process with respect to the eight musical tones is performed within one sampling clock. The memory storing this program is generally constituted of a ROM, so that the contents of the program cannot be changed later.
It is proposed that the memory includes a rewritable RAM, so that the program can be rewritten later as needed. This ensures that a single signal processing apparatus performs another signal process without its hardware structure being changed, thereby improving the general-purpose use of the apparatus. Further, during the processing of continuously-input signals, the signal processing apparatus can perform a different process on the signals to impart a quite different effect to the signals.
If the program is changed while running in the conventional signal processing apparatus, however, the algorithm of the signal processing is changed, thereby generating noise. In a process of adding reverberation to a musical tone signal as the above-described signal processing, for example, a program associated with reverberation to be produced should be stored in a program memory in order to alter the form of the reverberation. If a program corresponding to the program memory is rewritten to change from certain reverberation (reverberation 1) to another reverberation (reverberation 2), a parameter memory or a work memory in a DSP (digital signal processor), for example, sometimes has data before the rewriting of the program. Under such circumstances, even if only the program is changed, the data might be improperly converted so that an unexpected and undesired musical tone will be released.